Centrifuges and centrifuge cleaning methods

ABSTRACT

The drum of a centrifugal filter is cleaned by stopping the rotation of blades which normally rotate with the drum, while allowing the drum to continue to rotate, and retracting the bottom of the drum to open an annular aperture through which accumulated contaminants dislodged by the blades discharge.

BACKGROUND OF THE INVENTION

Centrifuges are known for filtering oil used as coolant during millingand other machining operations. The coolant, contaminated by metalparticles or shavings, is fed continuously into a rotating centrifugedrum. The contaminants accumulate against the peripheral side wall ofthe drum while the decontaminated liquid is collected as it dischargesthrough the mouth of the drum. The accumulated contaminants must beremoved at periodic intervals. However, known drums cannot be cleanedquickly or easily.

A primary object of the invention is to provide a centrifuge in whichthe drum can be cleaned quickly and without halting its rotation.

A further object of the invention is to provide a method of cleaning acentrifuge drum automatically without halting the drum or the flow ofliquid therethrough.

SUMMARY OF THE INVENTION

Briefly, and in accordance with the invention, the interior of the drumis provided with at least one cleaning member which in normalcentrifuging operation rotates together with a peripheral wall of thedrum. The cleaning operation is effected by causing the cleaning memberto stop rotating (or by otherwise establishing a speed differentialbetween the peripheral wall of the drum and cleaning member ) and byuncovering an opening in the lower part of the drum, whereupon thecontaminants are dislodged from the wall of the drum and discharged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic side view of a first embodiment of centrifugalfiltering apparatus,

FIG. 2 is a perspective view, partly broken away, of the drum andassociated parts of the apparatus shown in FIG. 1,

FIG. 3 is a view similar to FIG. 1 but of a second embodiment ofcentrifugal filtering apparatus,

FIG. 4 is a section taken on the axis of rotation, and showing the drumand associated parts of the apparatus shown in FIG. 3, the apparatusbeing depicted in its filtering mode, and

FIG. 5 is a view similar to FIG. 4 but showing the apparatus in itscleaning mode.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2 of the drawings, the apparatus shown thereincomprises a tank 1 for contaminated liquid, and in the upper part ofwhich is arranged a reservoir 2 for filtered coolant. In the base of thereservoir is a circular opening bounded by an upstanding wall 3. Pivotedto the tank at 4 is a support frame 5 provided with bearings for a shaftassembly 6 carrying the centrifuge drum 7. Also mounted on the frame isan electric drive motor 8 for rotating the shaft assembly 6 by way of abelt transmission 9. The drum has a peripheral side wall 14, the loweredge of which defines a discharge aperture closed by a movable bottomwall 10 supported by a link 11 pivoted on the frame. The upper side ofthe drum is formed by a plate rigid with the peripheral wall and havinga central orifice 13 larger in diameter than a supply pipe 15 throughwhich contaminated coolant is supplied from a tank (not shown) whichreceives the coolant from a machine tool or other working station. Theplate 12 is larger in diameter than the peripheral wall 14 and projectsradially outwards beyond the wall 3 so that during normal operation ofthe apparatus, filterd coolant discharges from the drum through theorifice and enters the reservoir 2. As shown in FIG. 2, the supply pipe15 has a vertical outlet pipe section 15a which passes through theorifice 13 and terminates near the botton of the drum. The shaftassembly 6 extends co-axially through the outlet pipe section 15a, asuitable seal being provided at the upper end of the outlet pipesection. Within the reservoir 2 is an outlet 16 to a tank for cleancoolant. A pumping system may be provided for returning to thecontaminated coolant tank any liquid which overflows into the tank 1from the reservoir 2 or which enters the tank during cleaning of thedrum in the manner shortly to be described. Within the tank is adraglink conveyor 17 for removing sludge deposited in the tank 1 duringthe cleaning operation.

The shaft assembly 6 consists of a set of co-axial shafts, notillustrated individually, one of which is drivably connected to annulardisc 18 connected by vertical bars 19 with the plate 12 which is rigidwith the peripheral wall 14. Another of the co-axial shafts has a collar20 carrying a group of equiangularly spaced vanes or blades 21 havingupwardly extending portions 21a, the radially outer edges of which arein contact with, or narrowly spaced from, the inner surface of theperipheral wall 14 of the drum and serve as scrapers for dislodgingaccumulated contaminants. A further shaft may be provided to drive theretractable bottom wall 10 or, instead, the bottom wall may be drivenfrom the peripheral wall 14 by suitable guides on which the bottom wallis slidable vertically. Alternatively, the bottom wall 10 may beundriven. The shaft driving the peripheral wall 14 and plate 12 isdriven directly by the pulley 22 of the belt drive 9, whereas the shaftdriving the vanes 21 is driven from the pulley 22 by way of anelectro-magnetic clutch 23. This latter shaft may be brought to a halt,or at least its speed reduced, by a brake 24.

The components of the apparatus mounted on the frame 5 may be madeaccessible for servicing by tilting the frame about the pivot 4 afterdetaching part of the reservoir.

In operation, contaminated coolant is supplied continuously through thepipe 15 to the lower part of the interior of the drum which rotates atabout 3,000 r.p.m. Centrifugal force throws the contents of the drumtowards the peripheral wall 14 where the solid particles are trappedwhile the filtered liquid escapes through the orifice 13 to flow acrossthe top plate 12 into the reservoir 2. Because the outlet pipe section15a discharges near the bottom of the drum, less dense particles, forexample particles of aluminium, are less likely to be carried away withthe filtered liquid than in known centrifugal filter apparatus. Thecentrifuging action of the drum is aided by the vanes 21 which, duringnormal operation, rotate at the same speed as the peripheral wall 14 andensure that the liquid moves at a constant speed. When accumulatedcontaminants are to be removed from the interior of the drum, either atpre-set intervals or in response to the operation of a sensor indicatingan appropriate accumulation of contaminants, the electro-magnetic clutch23 is de-activated so that the shaft driving the vanes 21 ceases to bedriven while the peripheral wall 14 and plate 12 continue to rotate. Thebrake 24 is operated to halt the vanes 21 which dislodge or scrape thecontaminants from the peripheral wall. Simultaneously, the bottom wall10 is retracted by the link 11 acted upon by a mechanism (not shown) toform an annular slot between the bottom edge of the peripheral wall 14and the bottom wall 10, the accumulated contaminants being driven outthrough the annular slot by the action of the stationary vanesco-operating with the spinning peripheral wall 14 of the drum. Removalof the contaminants is assisted by the flushing action of liquid whichcontinues to be supplied to the drum. The bottom wall 10 may cease torotate, or continue to rotate, depending upon the manner in which it isarranged.

Scavenging of the drum is completed in a matter of seconds and thebottom wall 10 is returned to its normal upper position and rotation ofthe vanes 21 re-started. Because the cleaning operation takes place soquickly there is no risk of the supply of coolant being interrupted andit is easily possible to meet the requirements of the machiningoperation by maintaining a sufficient quantity of coolant in the cleancoolant tank.

The tank 1 may be dimensioned to accommodate a number of centrifugedrums, the number of drums in use depending on, for example, theviscosity of oil to be filtered. Cleaning of the various centrifugedrums may take place in sequence or simultaneously. Alternatively, eachof a number of drums may be associated with a respective machine tool.

The second construction of apparatus will now be described withreference to FIGS. 3 to 5, wherein the same reference numerals are usedas in FIGS. 1 and 2 to denote the same components. In this apparatus,the tank 1 for contaminated liquid and the reservoir 2 for filteredliquid are arranged side by side, the tank 1 being surmounted by a cover30 in which is formed the opening for receiving the drum 7. The cover 30slopes down towards the reservoir 1 to enable filtered liquid dischargedfrom the drum to flow into the reservoir. Contaminated liquid suppliedfrom a working station is discharged direct into the tank 1 from a pipe31, and excess quantitites of tiltered liquid entering the reservoirpass into the tank 1 through an overflow 32. A pump 33 having an inlet34 draws up contaminated liquid from tank 1 and discharges it to aflexible supply pipe 15 of centrifuge drum 7.

The supply pipe 15 of this construction communicates with the interiorof a hollow support 15b in which is journalled the upper end of an innerhollow drive shaft 15a coupled to the bottom wall 10 of the drum 7. Apneumatic piston and cylinder unit 35 is coupled to the support 15b inorder to move it and shaft 15a between the raised position shown in FIG.4 in which the bottom of the drum 7 is closed and the lowered positionshown in FIG. 5 in which the bottom is open.

The hollow shaft 15a passes through an outer hollow drive shaft 6, andis driven therefrom by a clutch 23. The outer shaft 6 is supported onbearings 36 and driven continuously in rotation when in use by a motor 8through belt transmission 9. The outer shaft 6 is fast with the coverplate 12 of the drum 7, the plate 12 having a circumferentiallyextending ring of orifices 13 for the discharge of filtered liquid.

The bottom wall 10 is of frusto-concial shape and has mounted thereonthe vanes 21 which, in this construction, are each of substantiallytriangular shape.

The motor 8, piston and cylinder unit 35, and bearings 36 are mounted ona main frame structure 37 supported about tank 1. Brackets 38 projectdownwardly from the structure 37 and support a stationary friction pad39 of a brake 24. Pad 39 co-operates with a pad 40 on the underside ofbottom wall 10 when the bottom wall is lowered into the position shownin FIG. 5, for the purpose of braking the bottom wall 10 and vanes 21.

Operation is similar to that of the first-described construction. Duringoperation, the plate 12 and peripheral wall 14 are driven from the shaft6 which is connected to the plate 12 directly. When the apparatus is inthe filtering mode shown in FIG. 4, the bottom wall 10 and vanes 21 aredriven from the inner shaft 15a through clutch 23 from the outer shaft.Contaminated liquid is drawn from tank 1 by pump 33 and enters the drumthrough pipe 15, hollow support support 15b and hollow shaft 15a.Filtered liquid discharges from orifices 13 to flow down cover 30 intoreservoir 2.

To enter the cleaning mode, a control device responsive to a timer orsensor extends piston and cylinder unit 35 to lower shaft 15a and bottomwall 10, pipe 15 flexing slightly to permit this movement. The clutch 23disengages drive to the inner shaft 15a and the friction pads 39, 40engage and bring the bottom wall 10 and vanes 21 to a halt, therebyscraping accumulated contaminants from the inner surface of wall 14 andscavenging the drum.

In a modification of this construction, the inner shaft is undriven andthe bottom wall 10 is driven frictionally from the peripheral wall 14during the filtering operation.

Modifications may be made to either arrangement illustrated. Thus, forexample, there are many alternative ways of driving the drum and vanesdifferentially when required for cleaning. Similarly, other methods ofopening a discharge outlet in the bottom or lower end of the drum may beused. Other means may be provided for removing the sludge from thetank 1. The apparatus may be made from any suitable material, althoughnylon is thought to be especially suitable for the vanes and bottom wall10. It is possible for there to be a certain amount of slip between thevanes and the drum during normal filtering operation, it being of theessence that during cleaning there is established a speed differentialsuch as to dislodge the accumulated contaminants. Instead of physicallyretracting the bottom wall 10, it may be allowed to descend under itsown weight, following retraction of a bottom wall support. Otherarrangements may, of course, be provided for opening an aperture topermit discharge of contaminants. Thus, the drum may have a fixed bottomwall, and an annular closure member covering part annular slots in theperipheral drum wall, the closure being raised to open the slots.Conceivably, a cleaning member which is movable relative to the drum,other than in a rotational sense, may be used in combination with one ormore closable contaminant discharge apertures.

I claim:
 1. In a centrifuge comprising a drum, a drive system forrotating the drum, an inlet for supplying contaminated liquid to thedrum, the drum having at least one orifice in its upper part to permitthe discharge of filtered liquid; the improvement comprising anapertured lower end to the durm, a closure movable between a position inwhich said aperture is closed by the closure and a position in which theaperture is open, a cleaning member disposed within the drum formovement relative to the axis drum; means for effecting displacement ofsaid closure into its position uncovering the aperture during a cleaningoperation, and means for establishing relative movement between thecleaning member and the drum during such cleaning operation, said drumhaving a peripheral wall drivable continuously in rotation by the drivesystem, the lower end of said wall defining said aperture, said closurebeing constituted by a bottom wall movable parallel to the axis of thedrum between a raised closed position and a lowered open position.
 2. Acentrifuge according to claim 1, said peripheral wall and said bottomwall being drivable independently of each other by coaxial shaftsdrivably connected with each other through a clutch.
 3. A centrifugeaccording to claim 2, said cleaning member comprising a plurality ofvanes, means being provided for driving the vanes at substantially thesame speed as the drum during filtering and for halting the vanes duringthe cleaning operation.
 4. A centrifuge according to claim 3, said vanesbeing mounted on said closure.
 5. A centrifuge according to claim 4,further comprising a tank for containing contaminated liquid, a wallsurmounting the tank and having therein an opening within which saiddrum is located.
 6. In a centrifuge comprising a drum, a drive systemfor rotating the drum, an inlet for supplying contaminated liquid to thedrum, the drum having at least one orifice in its upper part to permitthe discharge of filtered liquid, the improvement comprising a wallmember having therein a circular aperture within which said drum isdisposed, means for collected filtered liquid discharged onto said wallmember from the drum via said at least one orifice, a tank disposedbeneath said wall member for receiving contaminated liquid; said drumhaving a peripheral wall and being open bottomed, a closure for saidopen bottom, means for displacing said closure from a position closingsaid open bottom into a position defining an annular aperture, during adrum cleaning operation, and a cleaning member within said drum foreffecting discharge of accumulated contaminants through said aperture.